1. Field of the Invention
The invention relates to the field of airships and, in particular, to a non-ridged aerodynamic lift producing vehicle with improved lifting gas distribution such that center of buoyancy is more closely aligned with the center of gravity of the vehicle.
2. Description of Related Art
There are basically two main types of fully lighter-than-air vehicles; the ridged type or as it is more commonly called the "dirigible" and the non-ridged type or "blimp". Blimps basically comprise a single or multi-number of non-ridged gasbags wherein internal inflation pressure is used to form the external shape of the vehicle. A typical example of this design is found in U.S. Pat. No. 4,265,418 "Elongated Inflatable Structures For Flying Device Bodies" by M. Eymard the shape of the vehicle. The other basic type of lighter-than-air vehicle is the ridged design wherein an internal support structure is covered with a flexible material that serves as the outer skin. The vehicle may consist of a single gas chamber wherein the outer skin serves as the "gas bag" or can have numerous internal gasbags. An example of this concept can be found in U.S. Pat. No. 4,591,112 "Vectored Thrust Airship" by F. N. Piasecki, et al. However, both examples require that they be simultaneously loaded and unloaded in order to prevent the vehicle from "flying off." In fact, such vehicles must be tethered when on the ground during such operations. A particular limitation of the non-ridged design is that the cargo compartment and propulsion system must be mounted on gondola at the bottom of the vehicle. The gondola is typically supported by catenary cables or curtains attached to the top of the gasbag. The dirigible design allows most if not all these components to be mounted within the main body of the vehicle; although most all incorporates a gondola of some sort. However, when the vehicle is extremely large there costs become prohibitive because the complexity of the internal structure. A problem with both designs is that, as fuel is consumed, the vehicle becomes lighter.
These two examples are true lighter-than-air vehicles in that the gas filled balloon generates all the lift. However, having the external contour of the vehicle in an aerodynamic lift producing shape can reduce the overall size of such vehicles and generally cost, for any given payload. Such aircraft are not totally buoyant and take off in a manner similar to a conventional aircraft. In such designs, it is common practice to use a ridged internal frame (the dirigible concept) in order to maintain the proper contour. For example U.S. Pat. No. 3,486,719 "Airship" by J. R., Fitzpatick, Jr. While the Fitzpatick, Jr. design uses a ridged skin, most use a flexible gasbag with an internal frame structure.
Of course there are non-ridged designs such as disclosed in U.S. Pat. No. 2,778,585 "Dynamic Lift Airship" by D. B. Tschudy. D. B. Tschudy's design includes a multi-lobe gasbag with a general aerodynamic shape, formed by catenary cables extending between the upper and lower surfaces of the vehicle.
However, there are problems with such vehicles, especially when they are very large. The generation of dynamic lift from the gasbag the vehicle creates bending in the gasbag, which are much greater than found in conventional fully buoyant vehicles. Secondly, the lift-generating body is much more aerodynamically unstable and therefore requires much larger tail surfaces than conventional vehicles, which in turn creates even greater loads on the air bag. These two factors would tend to point toward the use of a ridged internal structure. However, it has been found designing a ridged internal structure that's light enough and simple enough to produce at a reasonable cost does not appear to be feasible at the present time. Thus a pressure-stabilized structure appears to provide the only viable solution.
Prior art approaches such as disclosed by D. B. Tschudy addresses the above issue in that a metal support structure at the rear of the airship gas bag is used to absorb and distribute loads induced by the elevators into the gas bag. However, it is a complicated assembly. The three main lobes terminate in the same plane and the support structure includes 3 connected cup shaped caps that attach to the ends of the three lobes. While such an approach provides some benefit, it would have insufficient effect in very large vehicle. In addition, it does address the issue of the need to align the center of buoyancy with the center of gravity.
Thus, it is a primary object of the invention to provide a non-ridged partially buoyant vehicle having a low drag shape.
It is another primary object of the invention to provide a non-ridged partially buoyant vehicle that allows the vehicle mass and buoyancy centers to align while providing additionally providing increased support for large tail surfaces.
It is another primary object of the invention to provide a non-ridged partially buoyant vehicle that has an improved tail assembly load distribution system.